1. Field of the Invention
The present invention relates to the selective vapor phase chlorination of polychlorinated .beta.-alkylpyridines to produce useful higher chlorinated compounds and/or intermediates. More specifically, the invention relates to the selective gas phase chlorination of chlorinated .beta.-picolines to produce 2,3,5,6-tetrachloropyridine, and other useful chemical intermediates, e.g. to produce commercial insecticides or herbicides.
2. Description of Related Art
2,3,5,6-Tetrachloropyridine and 2,3-dichloro-5-(trichloromethyl)pyridine are chemical intermediates which are very useful in the production of commercial insecticides and herbicides.
A number of processes are known to produce 2,3,5,6-tetrachloropyridine (Sym-Tet), usually by liquid phase chlorination. When vapor phase chlorination without catalyst is used, the yields and selectivity of chlorination are poor and the reactions are relatively slow. Further, because of the lack of selectivity, a significant amount of by-products and waste products are formed.
Some references of interest include:
H. Johnson et al. in U.S. Pat. No. 3,186,994 disclose the vapor phase chlorination of alpha-picoline to produce alpha-trichloromethyl pyridines.
J. A. Corran in U.S. Pat. No. 3,370,062 discloses a gas phase chlorination to produce pentachloropyridine. Suitable staring materials include pyridine and methylpyridines. Porous materials such as silica, alumina or combinations thereof can be used. 2-Methylpyridine is chlorinated in the presence of silica to produce pentachloropyridine.
W. H. Taplin III in U.S. Pat. No. 3,420,833 discloses the vapor phase chlorination of pyridine and isomeric picolines (e.g. alpha and gamma).
R. Nishiyama et al. disclose in U.S. Pat. No. 4,241,213 that 2-chloro-5-trichloromethyl pyridine is produced by reacting beta-picoline with chlorine in a gaseous phase at 300.degree.-500.degree. C. The reaction can be carried out in the presence of a porous material, e.g., silica, alumina, silicon carbide.
R. D. Bowden et al. in U.S. Pat. No. 4,205,175 disclose the vapor phase preparation of partially-chlorinated derivatives of 3-methylpyridine having a single chlorine atom substituted for hydrogen on the pyridine ring and 2 or 3 chlorine atom substituents on the methyl group.
J. Perettie et al. in U.S. Pat. No. 4,281,135 disclose the liquid phase chlorination at about 220.degree. C. at about 50 psig of 2,6-dichloropyridine in the presence of alumina, iron or silica to produce 45% of 2,3,5,6-tetrachloropyridine.
G. Whittaker in U.S. Pat. No. 4,429,132 discloses the reaction of chlorine in the vapor phase with 3-methylpyridine at 225.degree.-325.degree. C. to produce 3-(trichloromethyl)pyridines in the presence of a metal oxide or metal halide catalyst. The catalyst may be a chloride or an oxide of copper, silica, magnesium, calcium, zinc, etc. Inorganic and organic gaseous diluents can be used.
K. Kujikawa et al. in U.S. Pat. No. 4,490,534 disclose a process to produce 3-chloro-5-(trifluoromethyl)pyridine. The chlorination takes place in a reaction zone in a reactor. The catalyst may be comprised of iron, antimony, copper or zinc chlorides, optionally on a carrier such as carbon, zeolite or pumice. The examples only describe trifluoromethyl reactants and trifluoromethyl containing products.
J. Sharvit et al. in U.S. Pat. No. 4,752,644 disclose the preparation of 2,3,5,6-tetrachloropyridine by direct chlorination of alpha-picoline in the gas phase with chlorine at about 200.degree. C. in the presence of water and a catalyst.
M. A. DesJardin et al. in U.S. Pat. No. 4,785,112 disclose a process for the vapor phase chlorination of 2,6-dichloropyridine to produce 2,3,6-trichloropyridine selectively over isomeric 2,4,6-trichloropyridine. 2,3,6-Trichloropyridine, when chlorinated, produces symmetrical 2,3,5,6-tetrachloropyridine in high selectivity over isomeric unsymmetrical 2,3,4,6-tetrachloropyridine.
J. Sharvit et al. in U.S. Pat. No. 4,810,797 disclose the preparation of polychlorinated pyridines by reacting chlorine in the gas phase with partially chlorinated pyridines at about 200.degree. C. in the presence of a catalyst, e.g. pumice and a Lewis acid halide.
I. Sangyo in Japanese Kokai JP 58,206,564 (Chem. Abst., Vol. 100, 138965j (1984) discloses the vapor phase catalytic chlorination of chlorinated pyridine derivatives. 2,6-Dichloropyridine, carbon tetrachloride and chlorine are contacted with solid ferric chloride/carbon catalyst at 220.degree. C. to produce 2,3,5,6-tetrachloropyridine (72.9%) and 2,3,6-trichloropyridine (8.8%).
All of the patents, references, articles, standards and the like cited in this application are hereby incorporated herein by reference.
None of these references individually or as a group disclose or suggest the present invention.
It is extremely useful to have a vapor phase selective chlorination of a polychlorinated .beta.-alkylpyridine (and/or .beta.-picoline) using chlorine in the presence of certain Lewis acid/or halide catalysts to produce 2,3,5,6-tetrachloropyridine and/or its precursors (including chlorinated picolines). The present invention provides such a process.